Parallel rule and protractor



Oct. 19, 1943. J. D. MACLEAN PARALLEL RULE AND PROTRACTOR Filed May 29, 1942 2 Sheets-Sheet l cFMHJw OMMW 2 Sheets-Sheet 2 J. MACLEAN Filed May 29, 1942 I PARALLEL RULE AND PROTRACTOR filial-IE...-

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Oct. 19, 1943.

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Fatented Oct. 19, 1943 PARALLEL RULE AND PROTRACTOR John Donald Maclean, Inverness, Scotland Application May 29, 1942, Serial No. 444,946 In Great Britain May 16, 1941 1 Claim., (Cl. 33-75) This invention relates to parallel rules and protractors and has for an object to provide an improved'construction of such rules or protractors facilitating the determination and reading off of degree angles. A further object is to provide a construction of parallel rule or protractor by which great accuracy of measurement of is provided on each of its longer sides with a da-'- tum mark from which the angles are set off on the three other edges, one series marked to 180 and the other from 180 to 360 and in order to prevent the same graduations being used to designate different degrees, a transverse slot is provided adjacent each end presenting a second edge which is marked off with the complemen- One of the edges of this slot may be bevelled for ease in marking off the angle on a map or chart. The outer edge of the rule or protractor may be bevelled for the same purpose. Suitably for convenience in reading off the angles one datum mark and the corresponding angles may be marked in one colour and the ing drawings in which Fig, 1 is a plan view and- Fig. 2 a section on the line 2-2 of Fig. 1 showing the invention applied to a parallel rule of the roller type while Fig. 3 is a plan view of the in vention'applied to a parallel rule of the split type. Figs. 4 and 5 are plan views of opposite sides of a protractor with the invention applied thereto.

As shown in the drawings, the improved parallel rule or protractor is provided with two datum points A on opposite sides and is marked along its bevelled outer edge Bfrom 0 to 360. Adjacent each end is provided a transverse slot C presenting a second bevelled edge D which as indicated in the drawings is provided with complementary markings and degree figures avoiding the need for the same graduations being used to designate different degrees.

In the case of the parallel rule the rule is preferably made of transparent material and the markings are engraved or otherwise provided on the lower surface E so that errors in observation due to parallax are avoided.

to nautical The rule shown in Figs. 1 andz is of the roller type, two grooved rollers F mounted on an axle (not shown) extending through openings in the body of the rule. The axle is supported for rotation in a suitably weighted metal casing G screwedor otherwise secured from the underside to the body of the rule. provided with projecting portions H presenting finger grips by which the rule can be easily moved to or fro over a map or chart.

The rule shown in Fig. 3 is of the split type with parallel links I andis adapted to be traversed over the map or chart in the manner usual with this type. In this type it is preferable to strengthen the rule and prevent accidental damage byv securing to the lower side of each half a plate as indicated at J which extends over the whole of the lower surface and slightly beyond the outside edges liable to be damaged.

In the protractor shown in Figs. 4 and 5 in addition to the transverse slots C there is provided a longitudinal slot L adjacent the edges of which on both sides of the protractor are marked useful scales so that the scaled distances or dimensions may be transferred direct from the edges of the slot to the map or chart without the need for using dividers on the scale to pick off the distances or dimensions and transfer them to the map or chart.

As shown also the face of the protractor not marked with degree angles is marked along one edge with a nautical miles scale of 1:500,000 and 1: 1,000,000.

Nautical miles to statute miles and kilometers miles conversion scales are also marked on the face.

Portions of the surface of the pro-tractor may be treated if required to provide a surface adapted for use in making calculations in pencil.

I claim:

An elongated parallel rule having a datum point on each of opposite sides, said rule having its side and end edges marked with graduations and scale markings designating degrees for less than 360", said graduations and scale markings extending entirely around the periphery of the rule, the rule having transverse slots adjacent each end, edges of said slots being marked with graduations and scale markings designating degrees supplementing the graduations and scale markings at the edges of the sides and ends of the ruleto provide graduations andscale markings on the rule for angles of from 0 to 360 without the same graduations being used in conjunction with different scale markings,

JOHN DONALD MACLEAN.

The casing is shown as 

